Fairy Rings - fungal lawn disease

A Fairy Ring is a lawn disease that is caused by certain types
of fungus. The effect and appearance of a fairy ring can vary depending
on what type of fungus is causing the problem but they generally
form one or more of the following:

A ring of toadstools on the lawn when there is sufficient moisture

One or more rings of deep green, lush looking grass

Areas of dead / yellowed grass or bare soil between the lush
rings.

Some may find the appearance of the toadstool only fairy rings
attractive, especially in a grassy
woodland environment. They can however cause serious problems on
a more formal lawn where the effects of dead grass, bare patches
and uneven colouring and grass growth can significantly impact on
a lawns appearance.

What causes fairy rings to appear?

Fairy rings are the result of certain types of fungi forming fungal
threads in the soil that the
turf is laid on. The most common fungus to cause fairy rings is
Marasmius Oreades. The threads that form are very densely packed
and normally reach down so soil depths of around 20cm although they
have been known to reach up to about 40cm. The effect of these tightly
packed threads on the lawn is to effectively starve the grass roots
of both water and nutrients by inhibiting root growth and preventing
water uptake. The resulting lack of water will effectively kill
the grass in badly effected areas of the lawn and so yellow / brown
patches can appear. Bare patches of soil may appear on the lawn
where the grass has been dead a long time.

How can a Fairy Ring be treated?

Once a fairy ring is established on your lawn they can be very
hard to remove. To try and prevent the spreading of the fairy ring
you can carefully cut any of the toadstools off at their base and
place them in a container. Once you have collected all the toadstools
burn them. Do not put them on the compost heap or redistribute them
over the lawn or soil as they contain spores that will further the
growth of the fungi. Burning the toadstools will destroy the spores.

Another tip for preventing the spread of a fairy ring is to mow
the fungal infected area independently of the rest of the lawn.
That is make sure to collect the grass clippings seperately and
again burn them rather than adding them to the compost heap as they
can contain the fungal spores. After mowing the infected section
of the lawn you can use a fungicide to clean down the mower to kill
any spores on the mower that might be transferred to a healthy section
of the lawn.

Getting rid of fairy rings can be tricky. You may be able to use
a fungicide containing
dichlorophen that is suited for applying to lawns. Make sure to
check with the manufacturers
instructions for application and usage guidelines. You don't want
to kill off all flora and fauna!

One labour intensive way to restore your lawn is to literally replace
the infected part of the lawn by digging up the turf from the centre
to 18 inches outside the infected area. Once the turf is up discard
it and then dig up the infected soil that contains the fungal threads
to a spades depth. Discard this soil (not on the lawn and preferably
at a waste disposal site) and then fill the area with fresh uninfected
soil and re-sow or re-turf the now bare area of lawn.